This invention relates to the field of eye surgery, and in particular to a method and apparatus for measuring the depth of an incision or pocket in a patient's cornea.
Some surgical procedures for the correction of visual disorders require incisions in the patient's cornea. For example, U.S. Pat. No. 4,452,235 describes a method and apparatus for corneal curvature adjustment. The method involves insertion of one end of a split-end Intrastromal Corneal Ring (ICR) into an incision formed in the patient's cornea and movement of the ring in a circular path until the ends of the ring meet. The ICR's thickness relates to the degree of corneal flattening that can be obtained, to provide for correction of varying degrees of myopia. ICRs are made by Keravision, Inc. and are further discussed in U.S. Pat. No. 5,318,047, entitled METHOD FOR CORNEAL CURVATURE VARIATION, and issued to Davenport et al. on Jun. 7, 1994, which is hereby incorporated by reference. Similarly, U.S. Pat. No. 5,090,955 describes the adjustment of corneal curvature through the injection of a polymeric gel into an incision made in a patient's cornea.
Both of these corrective procedures require precise measurement of the depth of the pocket into which the gel or ICR is to be inserted. Both procedures require an initial measurement of the corneal thickness, typically employing an ultrasonic pachymeter. An adjustable-depth diamond knife then makes a peripheral incision to a depth that corresponds to a predetermined fraction of the pachymetry measurement at the incision's side. For example, to insert an ICR, the incision depth corresponds to 68% of the pachymetry measurement.
After the initial incision is made, at least one lamellar pocket is formed for insertion of the gel or ICR. Using conventional technology, the depth of the pocket is estimated using a set of mechanical corneal thickness gauges, such as those manufactured by KeraVision, Inc., the assignee of the present invention. These gauges feature gaps of different widths for measuring corneal tissue thickness, and thereby pocket depth. If the measurement indicates that the pocket is not deep enough into the corneal stroma, the diamond knife is used to make a slightly deeper incision in order to create a second pocket at a deeper level. This procedure is repeated until a corneal pocket of a desired depth is created. After the pocket is finally created, the pocket is further formed into a annular shape for injection of a polymeric gel or an ICR.
Measuring the depth of the corneal pocket is a critical step in ICR implantation and other corneal surgery procedures. The depth must be measured accurately since the depth of the implant can affect the resulting refractive change. Therefore, it is desirable to provide an accurate and dependable way of measuring the depth of corneal pockets that are used for refractive correction and other ocular surgery procedures.